The present invention relates to a filter cartridge which comprises an annularly closed filter medium having axial end faces provided with end disks and which is disposed on a support tube, as well as to a filter in which such a filter cartridge is installed.
Filter cartridges of this type are known. They are used, for example, for filtering lubricating oil in an internal combustion engine. An example of such a filter cartridge is disclosed in WO 98/05 403. The cartridge has the geometry of a regular cylinder. The support tube is made in two parts, which are inserted from the two end faces of the cartridge into the interior formed by the filter paper and are snapped together. When the cartridge is installed in a filter housing, a seal is formed between the unfiltered and the filtered side by means of sealing rings, which are arranged on the support tube.
The two parts of the support tube are interlocked by means of a snap connection. This design requires, however, that the filter cartridge be produced in a first step and the support tube inserted in a second step. Furthermore, due to shoulders formed at the end of the two support tube halves, the support tube must always be made in two parts, since the filter cartridge must be mounted between the shoulders. The seal of the mounted cartridge on the support tube is then produced by the inherent elasticity of the end disks, which rest directly against the outer shell of the support tube. The end disks are preferably made of a nitrile rubber sheet material which is thermally cured to form the filter cartridge.
It is an object of the invention to provide a filter cartridge with an annularly closed filter medium and end disks at its end faces, which forms a simple unit with a support tube mounted in the interior of the cartridge.
Another object of the invention is to provide a filter cartridge and support tube assembly that can be produced cost-effectively.
A further object of the invention is to provide a new filter design.
These and other objects have been achieved in accordance with the present invention by providing a filter cartridge having an annularly closed filter medium having end faces provided with end disks to form a seal and which has a support tube which is provided with inlet openings and has end areas which are connected to the end disks so as to form a seal, wherein, in at least one of the end areas of the support tube, a sealing ring is arranged with at least one sealing surface directed radially toward the interior of the support tube, and wherein the support tube is constructed in one piece and has an outside diameter dimensioned such that the support tube can be inserted into the filter cartridge from one side.
In accordance with a further aspect of the invention, the objects are achieved by providing a filter cartridge having an annularly closed filter medium having end faces provided with end disks to form a seal and which has a support tube provided with inlet openings and having end areas connected to the end disks so as to form a seal, wherein, in at least one of the end areas of the support tube, a sealing ring is arranged with at least one sealing surface directed radially toward the interior of the support tube, and wherein the support tube is constructed in one piece and at least one end area of the support tube is firmly connected to the adjoining end disk of the filter cartridge.
In yet another aspect of the invention the objects are achieved by providing a filter comprising a housing having an inlet and an outlet for a fluid to be filtered, and a filter cartridge as described above installed in the housing such that fluid flowing from the inlet to the outlet passes through said filter cartridge.
The support tube is inserted into the filter cartridge according to the invention in such a way that its end areas are connected with the end disks on the end faces of the filter cartridge so as to form a seal. This seal may be produced, for instance, by making the outside diameter of the support tube slightly larger than the relaxed inside diameter of the end disks. The mounted support tube slightly expands the elastic end disks, which creates the sealing effect.
Furthermore, within the support tube, a sealing ring is mounted at least on one side, the sealing effect of which is deployed radially inwardly starting from the inside wall of the support tube. Of course, additional axial sealing effects of the sealing ring can be utilized.
The support tube of the invention is made as one piece. This simplifies mounting the support tube within the cartridge, since fewer parts need to be handled. It also saves material because no snap connection is required to fix the support tube within the cartridge. It also makes the assembly more reliable, since there is no need to ensure that the snap connection interlocks. To enable the one-piece support tube to be pushed into the cartridge, its outside diameter must be dimensioned appropriately. This means that at least an end area of the support tube must be dimensioned so that it fits through the opening in the end disk. In other words, the outside diameter of this end area must be smaller, equal to or slightly larger than the opening in the end disk, but excess diameter of the support tube must be below the elastic limit of the end disk so that the disk can stretch over the tube without tearing. The filter medium must have the shape of a closed annulus to form an interior space for the support tube. The filter medium may be a folded filter paper, a wound-up or folded nonwoven material or a porous material. The annular filter medium does not necessarily need to have the form of a regular cylinder. Other shapes, e.g. an irregular or an elliptical cross section, are also feasible. Such configurations may offer advantages with respect to the mounting dimensions of the filter.
An alternative embodiment of the invention also provides for a one-piece support tube having at least one of its end areas is molded into the adjacent end disk of the filter cartridge. It is of course advantageous to mold both end areas into the corresponding adjacent end disks. This provides an elegant solution to the sealing problem between the end disks and the support tube. In this design, the respective integrally molded end area must have a zone that intersects with the spatial extension of the end disk. This may be accomplished, for instance, in that the inside diameter of the finished end disk is smaller than the diameter of the end area of the support tube. This creates a stable unit between end disk and center tube. The previously mentioned sealing ring in the interior of the support tube provides the seal between the unfiltered and the filtered side. This is why the connection between end area and end disk does not need to be radially elastic.
Of course, other joining procedures between end area and end disk are feasible. The support tube may for instance be friction welded to a thermoplastic end disk. Another alternative is to glue the end disk to the support tube. In contrast to the above-described alternative of the invention, however, the bond between end disk and support tube then can only be detached by destroying the cartridge.
In another embodiment of the invention, the end areas of the support tube are formed by elastic tongues whose ends are molded into the elastic end disk. This makes it possible to eliminate the sealing ring at this end of the cartridge, since the bond between the end disk and the support tube is sufficiently elastic so that the end disk can be used directly to provide a seal between the unfiltered and filtered side of the filter.
In a further embodiment of the invention, the sealing ring is mounted within the interior of the support tube in such a way that it does not touch the end disk of the filter cartridge. This makes it possible to isolate the sealing tasks between support tube and housing and between support tube and end disk and achieves a more a reliable seal.
In accordance with a further embodiment of the invention, the sealing ring is also embedded in the support tube. The sealing ring may be made, for instance, of needled felt and may be placed into the mold prior to injection molding of the support tube. This creates a reliable bond between the support tube and the sealing ring. The sealing ring may also be made of an elastomer. Alternative fastening methods include gluing the sealing ring to the support tube and/or inserting the sealing ring into a corresponding seat on the support tube with an interference fit. The excess dimension should be such that it reliably secures the sealing ring inside the support tube.
If the end areas of the support tube are molded into, e.g. embedded in the end disk, the sealing ring, if provided with a suitable geometry, can also be held by a form-fit connection, which is formed by the inner rim of the end disk. When the filter cartridge is manufactured, the sealing ring can then be loosely inserted and fixed by molding the support tube into the end disk.
The end disks may advantageously be made from a thermosetting nitrile rubber foil or sheet material. The use of this material for end disks of filter elements has been field-proven. The foil is applied to the end faces of the filter medium and heated. This causes the end disks to expand and the end faces of the filter medium to be sealed. After the nitrile rubber has hardened, it has sufficient remaining elasticity to ensure the desired sealing effect within the inside diameter.
In accordance with another embodiment of the invention, the support tube has a closed area starting from an end area. This makes it possible to influence the filtration behavior of the filter cartridge. Due to the one-part construction of the support tube, the closed area can be extended a long distance toward the opposite end area, since no snap connection is necessary within the interior of the support tube.
To enhance the fixation of the sealing ring within the support tube, a shoulder may advantageously be provided in addition. This also gives the sealing ring a defined installation site.
A filter using the filter cartridge according to the invention is also included within the scope of the invention.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.